1. Field of the Invention
The present invention relates to a magnetic tape cartridge having a structure which inhibits the rotation of a tape reel on which magnetic tape is wound, when the cartridge is not in use.
2. Description of Related Art
As a magnetic tape cartridge which is used as an external recording medium for computers and the like, a magnetic tape cartridge of the type in which magnetic tape is wound on a single reel and this reel is rotatably housed in a cartridge case has heretofore been known. This kind of magnetic tape cartridge is used for saving data of computers and the like, and needs to have a structure which is not disabled by impact such as dropping, because a huge amount of important information is recorded on the magnetic tape cartridge.
The above-mentioned single reel type of magnetic tape cartridge is provided with a reel lock mechanism which inhibits the rotation of the tape reel in order to prevent the slack of the magnetic tape due to the rotation of the tape reel in the inside of the cartridge case when the magnetic tape cartridge is not in use. This reel lock mechanism has different constructions corresponding to the kinds of magnetic tape cartridges, and, for example, an LTO (linear tape open cartridge) type of magnetic tape cartridge has a reel lock mechanism which is incorporated in the inside of the reel hub of a tape reel as shown in FIGS. 7 to 9.
FIG. 7 is an exploded cross-sectional side view of this kind of related art magnetic tape cartridge 101, FIG. 8 is a cross-sectional side view of the essential sections of the magnetic tape cartridge 101 which is not in use, and FIG. 9 is a cross-sectional side view of the essential sections of the magnetic tape cartridge 101 which is in use. In the magnetic tape cartridge 101, a single tape reel 105 on which magnetic tape (not shown) is wound is housed in the inside of a cartridge case 104 constituted by a top shell 102 and a bottom shell 103 which are joined together.
The tape reel 105 includes a reel hub 106 which serves as a core on which magnetic tape is wound, a top flange 107 joined to the top end of the reel hub 106, and a bottom flange 108 formed integrally with the bottom end of the reel hub 106. A ring-shaped chucking gear 109, which is engaged with a reel-rotating drive shaft of a tape drive apparatus (recording/reproduction apparatus) which is not shown, is formed on the central section of the outside surface of the bottom of the reel hub 106, and is exposed to the outside via an opening 110 formed in the central section of the bottom shell 103. On the inner peripheral side of the chucking gear 109, a ring-shaped metal plate 111 for magnetically securing the tape reel 105 to the reel-rotating drive shaft is fixed to the outside surface of the bottom of the reel hub 106 by insert molding.
A reel lock mechanism for inhibiting the rotation of the tape reel 105 when the magnetic tape cartridge 101 is not in use is provided in the inside of the reel hub 106. The reel lock mechanism includes geared walls 112 formed to extend uprightly from the top surface of the bottom of the reel hub 106, a lock member 113 having engagement teeth 113a which mesh with gear sections 112a formed on the top ends of the respective geared walls 112, a spider (reel lock release member) 114 for releasing the engagement of the geared walls 112 and the reel lock member 113, and a reel spring 115 disposed between the inside surface of the top shell 102 and the top surface of the reel lock member 113 and operative to urge the tape reel 105 toward the bottom shell 103 via the reel lock member 113.
The geared walls 112 have arc-like shapes as viewed in top plan view, and are respectively formed on the top surface of the bottom of the reel hub 106 at three locations spaced equidistantly apart from one another around the same circumference centered at the axis of the reel hub 106. The engagement teeth 113a of the reel lock member 113 which are opposed to the gear sections 112a of the geared walls 112 are formed on the bottom surface of the reel lock member 113 in a ring-like shape as viewed in top plan view, and are constantly urged by the reel spring 115 in the direction in which the engagement teeth 113a are brought into engagement with the gear sections 112a. A fitting projection 113c which has an approximately cross-like shape as viewed in top plan view is formed on the top surface of the reel lock member 113, and a fitting recess 102a which has an approximately cross-like shape as viewed in top plan view and in which the fitting projection 113c is fitted is formed at an approximately central section of the inside surface of the top shell 102.
The spider 114 has an approximately triangular shape, and is disposed between the bottom of the reel hub 106 and the reel lock member 113. A total of three legs 114a are formed on the bottom surface of the spider 114 so as to project downwardly from three vertices of the approximately triangular shape of the spider 114, respectively. When the cartridge is not in use, the three legs 114a are inserted in position between gears of the chucking gear 109 via insertion holes 106a formed in the bottom of the reel hub 106. A support surface 114b which supports a sliding contact section 113b having an arc-like cross-sectional shape formed to project from an approximately central section of the bottom surface of the reel lock member 113 is disposed on an approximately central section of the top surface of the spider 114.
When the related art magnetic tape cartridge 101 constructed in the above-mentioned manner is not in use, the reel lock member 113 is located at a lock position as shown in FIG. 8, and is forced by the urging force of the reel spring 115 so as to press the tape reel 105 against the bottom shell 103 and so as to engage the engagement teeth 113a with the gear sections 112a of the geared walls 112 and inhibit the rotation of the tape reel 105.
On the other hand, when the magnetic tape cartridge 101 is in use, the reel-rotating drive shaft of the tape drive apparatus which is not shown is brought into engagement with the chucking gear 109, whereby the legs 114a of the spider 114 inserted in the positions between gears of the chucking gear 109 are pressed upwardly into the inside of the cartridge case 104. Accordingly, the reel lock member 113 is moved to the lock release position shown in FIG. 9 against the urging force of the reel spring 115, so that the engagement between the gear sections 112a and the engagement teeth 113a is released.
Then, the tape reel 105 is integrated with the reel-rotating drive shaft by the action of magnetic attraction between the metal plate 111 and the reel-rotating drive shaft, whereby the tape reel 105 is rotationally driven via the chucking gear 109. At this time, the rotational operation of the reel lock member 113 is restricted by the action of fitting between the fitting projection 113c and the fitting recess 102a of the top shell 102, and the spider 114 rotates together with the tape reel 105 by means of a sliding contact action produced by the state of point contact between the support surface 114b disposed on the top surface of the spider 114 and the sliding contact section 113b of the reel lock member 113.
A related art document relating to the invention of the above-mentioned application is as follows:
Japanese Patent Application Publication No. 2002-343058.
When the above-mentioned magnetic tape cartridge 101 is not in use, the movement of the tape reel 105 in the horizontal direction of the cartridge case 104 (in the radius direction of the tape reel 105 is restricted not only by the reel lock action of the reel lock member 113 but also by the force of the reel spring 115 to press the tape reel 105 against the bottom shell 105 as well as the fitting action between the outer periphery of the chucking gear 109 and the opening 110 of the bottom shell 103.
However, if, for example, a dropping impact is applied to the magnetic tape cartridge 101, the tape reel 105 of heavy weight on which magnetic tape is wound shows an unstable behavior in the inside of the cartridge case 104. If an impact exceeding a certain magnitude is applied to the magnetic tape cartridge 101, the tape reel 105 may be moved in a horizontal direction relative to the cartridge case 104 to such an extent that the outer periphery of the chucking gear 109 climbs over the peripheral taper surface of the opening 110 and the engagement between the reel lock member 113 and the geared walls 112 is released. In this case, a deviation of not less than one pitch in gear engagement occurs between the gear sections 112a of the tape reel 105 and the engagement tooth 113a of the reel lock member 113, so that a deviation occurs between the axis of the tape reel 105 and the axis of the reel lock member 113.
If a deviation occurs in this manner between the axis of the tape reel 105 and the axis of the reel lock member 113, when the magnetic tape cartridge 101 is to be loaded and used in a tape drive apparatus, the chucking gear 109 is located in the state of being displaced with respect to the opening 110 in the direction of the deviation, so that there occurs the trouble that the reel-rotating drive shaft fails to appropriately engage with the chucking gear 109 and invokes the disablement of the magnetic tape cartridge 101 or causes the malfunction of the tape drive apparatus.
To address this trouble, for example, the above-cited Patent Document 1 discloses a construction in which a plurality of position restriction ribs 120 which are opposed to the outer periphery of the reel lock member 113 and restrict the axial deviation of the reel lock member 113 from the axial position of the tape reel 105 are formed to project, respectively, from locations spaced equidistantly apart from one another around the inner peripheral surface of the reel hub 106, as shown in FIG. 10. According to this construction, the relative movement of the tape reel 105 with respect to the cartridge case 104 due to, for example, dropping impact can be restricted by the action of abutment between the position restriction ribs 120 and the periphery of the reel lock member 113, whereby the deviation between the axis of the tape reel 105 and the axis of the reel lock member 113 can be restrained.
However, the construction described in the above-cited Patent Document 1 has the drawback that since the position restriction ribs 120 are formed continuously with the inner peripheral surface of the reel hub 106 made of an injection molded product of synthetic resin material, sink marks (depressions) are formed in the outer periphery of the reel hub 106 at locations corresponding to the formation positions of the position restriction ribs 120, so that the flatness of the outer peripheral surface of the reel hub 106 is damaged.
As mentioned above, the reel hub 106 constitutes a core on which magnetic tape is wound with multiple turns, so that if the flatness of the outer peripheral surface of the reel hub 106 which is a winding surface for magnetic tape is damaged, the inside layers of wound magnetic tape in particular undergo deformation.
If the flatness of the outer peripheral surface of the reel hub 106 deteriorates, the roundness of the reel hub 106 is impaired, so that rattling such as axial shaking of the tape reel 105 during high-speed rotation thereof increases and the stable runnability of magnetic tape cannot be ensured.